Multichannel telegraph system



Nov. 10, 1942. J. w. cox

MULTICHANNEL TELEGRAPH SYSTEM Filed Oct. 26, 1940 5 sheetssheet 1- Nov. 10, 1942.

J. W. COX

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Nov. 10, 1942.

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MULTICHANNEL TELEGRAPH SYSTEM Filed oct. 2e, 1940 5 sheets-sheet 5 anw-Puf p/L 72.-; PECPUEP Patented Nov. 10, 1942 MULTICHANNEL TELEGRAPH SYSTEM John W. Cox, Berkeley, Calif., assignor to Badia Corporation of America, a corporation of Dela- Ware Application October 26, 1940, Serial No. 362,905

1 Claim.

This invention relates to multiplex systems and is an improvement in certain respects on the invention disclosed in my application issued as Patent No. 2,264,510 on December 2, 1941.

An object of the invention is to provide a multi-channel system wi-thout synchronous commutating or distributor mechanism, by use of different channel frequencies when the marks occur at different times and the same frequency when the marks occur simultaneously,

Another object is to provide a multi-channel system without synchronous distributors by transmitting different modulating frequencies at different times, transmitting no signal current when such channels send mark signals simultaneously and transmitting a third and different frequency when the transmitters send space signals.

Other objects will appear in the following description, reference being had to the drawings, in which:

Fig. 1 is a diagrammatic illustration of the transmitter system.

Fig. 2 is a diagrammatic illustration of the receiving system.

Fig. 3 contains graphs illustrating the principle of the invention of Figs. 1 and 2.

Fig. 4 is a modified form of transmitting system.

Fig. 5 is -a receiving system for the modification of Fig. 4.

Fig. 6 contains graphs illustrating the principle of the invention of Figs. 4 and 5.

Fig. 'lis a modied form of receiver for the transmitter of Fig. 1, with cer-tain frequency adjustments.

Referring to Fig. 1, I and 2 indicate tape or other transmitters for two individual channels to be combined in multiple transmission, These are well known and have been shown as movable switch arms 3, make contacts 4 and blank contacts 5. Contact 4 of transmitter No. 1 is connected to resistance 6 and cont-act 4 of transmitter No. 2 is connected to resistance 1. 'I'hese two resistances are joined together and are con- I ing terminal of the neon tube. The battery, c'nni denser and neon tube constitute an oscillator, but various other oscillators may be used instead.

The secondary of the transformer I 0 is connected to any desired number of amplifiers, generally indicated by block diagram I2, as such The other teris impressed on the grid circuit.

The plate of tube I3 is connected to one terminal of load resistance I 6. The positive terminal of the B source is connected to the other terminal of the resistance, and the negative to the cathode of the tube.

The grid-cathode or input circuit of tube Il .is adjustably connected to load resistance I6, so that the signal voltage is applied negatively to the grid. The positive terminal of the B source is connected through resistance I8 to the plate of the tube and the negative terminal to the cathode. The grid circuit may have a negative bias source I9 for adjusting the grid potential to the desired point on the characteristic curve.

The plate of tube I1 is connected through the primary of radio frequency transformer 20 to the plate of tube 2|. This primary may be tuned to the radio frequency carrier by condenser 22. The grid-cathode circuit of tube 2| is connected to any desired radio frequency oscillator indicated by block diagram 23. The grid circuit may have the usual bias source 24 for regulation purposes. The cathode of tube 2l is connected to the negative of the B supply.v

The secondary of transformer 20 is connected to transmitting apparatus of well-known type indicated by block diagram 25, The output of the transmitting apparatus is connected to antenna 26 and to ground.

In Fig. 2 the receiving antenna 21 and the ground terminal are connected tol appropriate receiving apparatus consisting as usual of radio frequency amplifiers, detector and audio frequency amplifiers. The invention does not reside in these devices and any kind may be used. The receiving apparatus has thus been indicated in block diagram 28.

The output of the receiver 28 is connected in shunt to band-pass iilters 29, 30 and 3I of standard form, indicated in block diagram. The output of the filters is connected through transformers 32, 33 and 34 to rectiers 35, 36 and 31,

respectively, across the output terminals of which are respectively connected load resistances 38, 39 and 40. The output of the rectii'lersmay be ltered by condensers 4I, 42 and 43, respectively.

The input terminals of amplier tubes 44, and 46 are adjustably connected to the load resistances 38, 39 and 40, respectively. The input of a fourth amplier tube 41 is also adjustably connected to load resistance 40. All these amplifying tubes have suitable negative bias sources 48, 49, 50 and 5I to operate at any desired part of the grid voltage-plate current characteristic. If zero amplifier plate current is desired for signal spaces, these sources would have such value as to block the tubes except upon the arrival of a signal positively applied to the grid circuits Recorder 52 is connected in the plate supply of tubes 44 and 45 in parallel, so as to be operated when either of these tubes responds to the signal. Recorder 53 is likewise connected in the plate supply lead of tubes 45, 41 in parallel, for operation by either of the tubes.` 'The recorders may be of any type, such as the wellknown syphon recorder or a photo recorder.

The operationof my invention will now be explained:

When a mark is transmitted by tape transmitter I and a space by transmitter 2, resistance 6 will determine the voltage applied to condenser II and a definite frequency F1 will be generated by condenser II and neon tube IIa, in which is connected the primary of transformer I0. This condenser charges up to the breakdown voltage of the neon tube and discharges through the tube, as fully explained in my said copending application. Thus, a voltage of definite frequency F1, set by resistance 5, is applied to transformer I0.

When a mark is being sent by transmitter 2 and a space by transmitter I, resistance 1 will determine the charging time of condenser II and a different frequency F2 is produced.

When both transmitters send a mark simultaneously, resistances and 1 will be in parallel in the charging circuit of condenser II and, of course, will have a different value from either one alone. This will produce a third frequency F3 in the primary of transformer I5. When neither tape transmitter sends a mark, no current will flow to the condenser I I and both channels will send a space.

The signals of the two channels may be combined in any relation, but let it be assumed that channels No. 1 and No. 2 are sending the code letters N vand A, respectively, in the time relation shown in Fig. 3. Tape transmitter 2 will cause the condenser-neon tube oscillator to produce the frequencyFz, which after amplification at I2 will cause tube I3 to unblock on the positive half cycles, which will block tube I1 and apply voltage to tube 2I that will cause the radio carrier frequency to be radiated by transmitter 25 and antenna 25 in a well-known way. Radiation will continue during the positive half cycles of Fi throughout the time of the dot 54 (Fig. 3). That is. the radio carrier will be chopped at the frequency F2.

When point 55 is reached, channel No. 1 commences to send the dash of letter N and transmitter channel No. 2 starts the space following dot 54. Resistance 5 now sets the frequency and the radio carrier will be chopped at frequency F1. When the point 55 is reached, both channels will be transmitting and the parallel resistances 5 and 1 will set a new frequency Fa. The radiated wave will then be chopped at frequency F3 up to the point 51, when channel No. 1 commences its space. From point 51 to point 58, the radiated wave will be chopped at frequency F2. IAt this point channel No. l sends a mark and channel No. 2 a space. Therefore, the radiated wave will be chopped at frequency F1 and this will continue to the point 59.

At the receiver the radiated wave is received, detected and amplied andin the output circuit there will be three frequencies, F1, F: and F3, occurring at different time intervals. as shown by Fig. 3. Frequency Fa can pass only through the band-pass filter 35. After rectification and mteringit as and 42, the dot pulse s4 unblocks tube 45 and Arecorder 53 produces a dot. Recorder 52 at this time produces a space, as the frequency F2 cannot pass either band-pass nlter 29 or 3|. If-thev bias used is not a blocking bias,

the same result will be produced.

When point 55 is reached, frequency F1 passes through band-pass filter 29 and unblocks tube 44, thus producing a mark portion in the dash of letter N. During this period the recorder 53 produces a space, as frequency F1 cannot pass through filters 30 and 3I.

When point 55 is reached, frequency F3 passes through filter 3| and unblocks both of the tubes and 41. The current in tube 45 causes recorder 52 to produce the remaining portion of the mark of the dash in letter N and tube 41 causes recorder 53 to simultaneously produce the rst `part of the dash in letter A.

At point 51, frequency F2 passes filter 30 only land recorder 53 nishes the mark of the dash of letter A while the recorder 52 produces a space. At point 58, the arrival of the signal of frequency F1 similarly causes recorder 52 to produce the dot of letter N while recorder 53 produces a space.

It is thus seen that channels No. l and No. 2 can transmit independently of each other without synchronizing apparatus or distributors and the channel recorders will faithfully produce the separate messages.

The oscillator need not be the condenser-neon tube type, as this has been described by way of example. Also, the modulator need not be of the type disclosed. The signals can modulate the radio carrier Wave in any way desired. I'he chopping system is a satisfactory form of modulation and it was described as an example only.

At the receiver, tube 41 may be omitted and recorders 52 and 53 fed in parallel from the output of tube 45. Also, mechanical types of relays xnay be used in the place of tubes, if desired.

In the modification of Figs. 4 and 5, the reference characters I to I2, inclusive, indicate the same parts in the drawing as those used in Fig. l and these parts have the same functions as those of Fig. 1. However, the switch arms or tongues and contacts' of the tape transmitter are differently connected in some respects, as will now be indicated.

` The tongues 3 of the two transmitters are connected together and to one of the ends of resistances 5 and 1 and also to potentiometer resistance 9. 'I'he mark contact 4 of transmitter I is adjustably connected to both resistances 5 and 1. 'I'he mark contact 4 of transmitter 2 is connected to the other, or potentiometer, end of resistances 5 and 1. The space contacts 5 of both transmitters are connected together and to 4the junction point of condenser II and to the primary of transformer III through a resistance 1a, which may represent merely the inherent resistance of the condenser circuit outside of resistances 5 and 1. In all other respects the connections of Fig. 4 are the same as in Fig. 1, except that the keying and modulating apparatus 5I! is shown in block diagram. This may be understood to contain all the parts I4 to 24 shown in Fig. 1, or the parts of any other known modulator.

In the receiver 28 of Fig. 5 all the apparatus referred to in connection with Fig. 1 will be used.

but the mark portion 65 wm continue, sincecur-- 'I'he output of the receiver is connected to the three band-pass filters 6l, 62 and 63, and the output of these are respectively connected to rectiers 35, 36 and 31, as in Fig. 1. For simplicity of explanation and illustration, I have shown the rectiers connected to electromagnetic relays, but it will be understood that the amplifying stages 'shown in Fig. 2 may be used instead, as they would act in the same way.

The operation of the modification of Figs. 4 and 5 will now be described:

Referring to Fig. 4, when transmitter I sends marks with transmitter 2 sending spaces, resistance 6 will be short-circuited and the battery current will iiow through resistance 1, mark contact 4 and tongue 3 of transmitter No. 1, tongue 3, space contact 5 of transmitter No. 2 and resistance 1a to the condenser Il. Resistances 1 and 1a will thus determine the oscillation frequency F1. When the transmitters both are sending marks, no current can iiow to condenser Il and no frequency is generated.

When transmitter No. 2 sends a mark and transmitter No. 1 sends a space, current ows from the potentiometer slider through the mark contact and tongue of transmitter No. 1 and the tongue and space contact of transmitter No. 2 to the condenser il through resistance 1a. Thus, resistance 1a determines the frequency F2.

When both transmitters are sending spaces, current will flow through resistances 1 and 6,

rent flows to' recorder 8i through contact 61.

'I'he foregoing explains how marks and spaces are produced under all possible conditions and the completion-.of the letter zS need not be referred to. 1t will be noted that the recorders,

when idle, record a line having the amplitude of i the marks instead of that of spaces, as is lusual, though, of course, when the circuit is idle for any length of time the" switches 89 may b'e operated to disconnectthe power from the recorders.

If vacuum tubes are substituted for the mechanical relays in Fig. 5, they will secure the same result in exactly the way already described,

as will be apparent from the explanation in connection with Fig. 2.

The broad band-pass "filter 62 maybe omitted, but is is preferred, since it will exclude interference occurring outside the band covered by F1, F2 and F3.

Fig. '1 shows a modified receiver for the signals transmitted by Fig. 1, with proper adjustment of the resistances 6 and 1 to produce the desired,

frequency F1, F2, F3. By way ofi example, assume that when channel No. 1 sends a mark separately, the frequency 'F1 will be 900 .cycles per second; when channel No. 2 sends a; mark separately, the frequency F2 will be 1,000 and the tongue and space contact of the transmitters in parallel and resistance 1a to the condenser.'

These three resistances will determine the oscillation frequency F3.

The foregoing give the only possible connections in transmitting two signals independently' of each other.

Let it be supposed that transmitter No. 1 is sending Morse code letter A and transmitter No. 2 Morse code letter S in the chance time relation indicated in Fig. 6. Both transmitters will be starting with spaces. This will produce frequency F3, which will modulate the radio carrier and be received at receiver 28. The extracted frequency F: can pass only through wide band-pass filter 62. The rectified current of 36 will operate both relays 64, 65 and open the normally closed contacts 66, 61. This will form the spaces 68, 69.

At the point 10, both tape transmitters will be sending marks and no modulating current is produced. At the receiver there will, therefore, be no potential applied to the band-pass filters. None of the relays will be operated, but since contacts 56 and 61 are normally closed, the recorder will have its circuit closed and will record the marks 1|, 12.

'I'he spaces at 13, 14 will be recorded by frequency F3, as already explained. Likewise, mark portions 15 and 15 will be produced by absence of any signal.

When portions 11 and 1l are reached, Fi will be transmitted and recorded. This will pass only filters 6| and 32. Relays 13. 34 and 65 will thus operate. This will record al mark in recorder 33 and a space in recorder 3|. Portions 32, 33 willbe recorded by absence of a signal, as already explained. but when portions 34, are reached,

frequency F: will be sent out and received through filters 52 and 63. This will operate relays 64, 35 and 35, closing contacts 31 and opening contacts 33 and 31. Thiswillproduce a space .34- in recorder, as the circuit is interrupted.

when both channels mark together, the frequency Fa will be 500. With these assumed values, band` pass nlter 9,0 will be designed to p ass frequencies 500 to 900, inclusive, and filter 9| to pass a fre-Y quency of 1,000.

' 'In the signals 0f Fig. 3, the initial dot 54 would be transmitted and received as frequency Fa, or 1,000. 'This frequency will be able to pass filter 9| only. Thus, a dot will be recorded in' recorder v 53 and a space will be recorded in recorder'5'2. Between points 55 and 56, the frequency sent and extracted will be F1, or 900. This will pass lter and record a mark portion in recorder 52.-

Recorder 53 will record .a space at this time. At

point 56, a frequency F3, or 500, will be sent and extracted. The frequency of 500 will pass through filter 90 and a mark will be recorded by recorder 52. The second harmonicf the frequency Fs, or 1,000, will, of course, pass lter 3l and a mark portion will be recorded by recorder 53, sincel the signals will inherently have a sufficient amount of harmonics. Further explanation will be unnecessary, as it will now be apparent how any signal will be sent and'recorded for each channel in this modification.

It will not be necessary to use the second harmonic of the frequency lib.` By proper choice of values, other harmonics may be used. is Having described my invention, what I claim In a two channel system, the method of receiving signals having fundamental and inherent harmonic components of a rst frequency when one channel alone is transmitting, a second frequency when the two channels are transmitting simultaneously. and a third frequency, harmonic to said second frequency, when the other channel alone is transmitting, which comprises passing the first and second frequencies to one indicator through a filter having an upper cut-of! below said third frequency, and passing the inherent harmonic of the secondfrequency and said third frequency to another indicator through a filter having a lower cut-oi! above the first frequency.

JOHN W. COX. 

